I've just bought one. It's very nice ;-)
Obviously, the shuffle comes with the usual impeccable Apple styling, both in the box and the product. The actual shuffle is really small and light (so small it fits in the belt loop of my jeans, making it very unobtrusive!). It's the sort of thing you can slip into your pocket without really noticing. It comes with a "lanyard" (neclace, to you and me), which I can sort of imagine using. You also get the swanky white ipod headphones.
I bought the shuffle to upgrade/replace an MPIO I have. It's a 256MB thing, which I've found a bit small, unless you use WMAs (which you need to create at a slightly lower bit rate). That's a pain as my whole collection is MP3, so I'd have to duplicate it all. Also just using the MPIO isn't really that easy (in the sense that loading it up can only be done on Windows with some not-too-great software).
In comparison, the shuffle is really good. It uses iTunes, which can automatically fill it up with random stuff from your collection (or a playlist, if you prefer). Alternatively, you can just copy tracks to it as you normally would (it'll play them in the order you save them, or shuffle them if you want). The really cool thing is iTunes will transcode your music into 128K AAC files (which are smaller than the equivalent MP3s and such like). That's really really cool, because you don't take up as much space on the shuffle as you do in your actual collection (where of course, high quality MP3s are what you want). If you don't fancy using iTunes, then gtkPod will do it under Linux (on my Fedora 3 system, the shuffle is automatically detected and mounted, so instantly available to gtkpod).
In terms of actual usability, it "does what you want". It blinks lights at you in different colours to tell you what it's doing, which is a bt cryptic, but makes plenty of sense really. For actual use, it does what you'd expect, forward, back, play, pause. Not sure you really need a lot more than that. The lack of a screen isn't really that much of a problem, I mean, if you're doing something and you want to skip a couple of tracks, do you really need one? I think not.
One slight downside is that the shuffle works quite slowly. That is, clicking "forward" to skip a track has a slight delay, so you can't move through tracks very quickly (although multiple clicks skips more than one track). Also, there's a short silence between tracks (which you don't get on a proper iPod or in iTunes). That said, this isn't exactly a debilitating problem.
So all in all, it's a very nice little gadget. There's no doubt it could be better in certain ways, but in reality, it does what you need very well. Well worth it.